A semiconductor device including a semiconductor element-bearing substrate (1a, 1b) provided with a semiconductor element (3) and a heat sink (2) bonded to the substrate is described in FIG. 1, FIG. 2, and the like of PTL 1 below. In addition, technologies to form a slit and a groove in a heat sink are described in PTLs 2 to 4 below.
The semiconductor device described in PTL 1 below has a problem in that mountain-like thermal distortion occurs, which is a warp resulting from a difference in thermal expansion coefficient between the semiconductor element-bearing substrate and the heat sink, as described in the paragraph [0004] and FIG. 3 of PTL 1. In the state in which mountain-like thermal distortion has occurred, for example, such problems as described in the following items (i) and (ii) may occur.
(i) Firm fixation between the heat sink and a member which is bonded to the heat sink (hereafter referred to as a “member to be bonded”) becomes difficult and, for example, an electronic part directly or indirectly bonded to the heat sink may be peeled.
(ii) The heat sink may be damaged by generation of a thermal stress between the heat sink and the member to be bonded.
A technology aiming at suppressing the above-described mountain-like thermal distortion and problems thereof will be described below.
PTL 1 describes a technology aiming at suppressing the mountain-like thermal distortion of a heat sink by appropriately selecting the material for solder to bond the heat sink to a semiconductor element-bearing substrate serving as a member to be bonded. However, in some cases, this technology cannot suppress the mountain-like thermal distortion sufficiently.
PTLs 2 to 4 describe technologies aiming at suppressing mountain-like thermal distortion by forming slits or grooves in a heat sink. These technologies aim at absorbing relaxing the mountain-like thermal distortion by dispersing the mountain-like thermal distortion, which is a wide-area distortion of the whole heat sink, into local distortions.
However, the technologies described in PTLs 2 and 3 have a problem in that thermal diffusion in the plate surface direction orthogonal to the plate thickness direction of the heat sink is hindered. For details, in the technology described in PTL 2 (refer to FIG. 2 and FIG. 3), a plurality of slit holes extending parallel to each other are disposed in the heat sink. Also, in the technology described in PTL 3 (refer to FIG. 1 and the like), arc slits along the circles centering on the center of the heat sink are disposed in the heat sink. According to these technologies, thermal diffusion in the direction crossing the slits may be hindered by the slits. If the thermal diffusion is hindered, as a result, insufficient suppression of the mountain-like thermal distortion of the heat sink may occur.
Meanwhile, in the technology described in PTL 4, the heat sink and the member to be bonded may be peeled. For details, in the technology described in PTL 4 (refer to FIG. 2, FIG. 4, and the like), grooves are disposed in the surface and the back of the heat sink alternately and, therefore, the grooves are arranged in, so to speak, a staggered configuration. In this technology, the mountain-like thermal distortion of the heat sink is absorbed relaxed by converting the mountain-like thermal distortion of the heat sink to bellows crease deformation of the heat sink and rotation of the center portion of the heat sink. However, a stress or strain, which induces peeling between the heat sink and the member to be bonded, may be generated by the bellows crease deformation of the heat sink.